There are three major impediments to making beta cell allotransplantation clinically feasible in Type I diabetics: limited human tissue supply, allorejection, and recurrent autoimmunity. We have recently demonstrated that adult human pancreatic Beta-cells can be successfully transduced with integrating lentiviral vectors, making it possible for the first time to optimize genetic engineering strategies to overcome these impediments. In this application, it is proposed: (1) to create conditionally immortalized beta cell lines from mouse, pig, and human islets, using loxP-flanked bicistronic transgenes expressing insulin-promoter-driven candidate immortalizing genes and an internal ribosome entry site-controlled suicide gene (TK) to destroy any proliferating cells after excisional inactivation by a Cre recombinase- expressing herpes simplex virus-derived viral vector; (2) to express in primary human beta cells (using both HSV and then lentiviral vectors) two viral genes (ICP 47 and US11) that downregulate human cell-surface class I major histocompatibility complex molecules in order to prevent allorejection by MHC class I-dependent T cell responses and then to quantitate the extent of MHC downregulation; (3) to express in primary human beta cells (using lentiviral vectors) two complementary antiapoptotic genes (Bcl-2 and p35) in order to prevent allorejection by MHC class I-independent T-cell responses; and (4) to assess the sensitivity to allogenic rejection of primary human beta cells stably transduced with ICP47, and/or US11, and/or Bcl-2, and/or P35, using the recently developed hu-PBL-NODscid mouse model.